diff --git a/app/src/main/cpp/api.cpp b/app/src/main/cpp/api.cpp
index 8472282..6c06861 100644
--- a/app/src/main/cpp/api.cpp
+++ b/app/src/main/cpp/api.cpp
@@ -15,6 +15,8 @@
 #include <openssl/asn1t.h>
 #include <openssl/asn1.h>
 #include <openssl/x509.h>
+#include <openssl/ecdsa.h>
+#include <openssl/bn.h>
 
 #include "api.h"
 #include "consts.h"
@@ -448,6 +450,25 @@ ASN1_SEQUENCE(EncapsulatedContent) = {
 } ASN1_SEQUENCE_END(EncapsulatedContent)
 IMPLEMENT_ASN1_FUNCTIONS(EncapsulatedContent)
 
+#include <openssl/opensslv.h>
+
+#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+typedef struct ECDSA_SIG_st {
+    BIGNUM *r;
+    BIGNUM *s;
+} ECDSA_SIG;
+
+typedef struct bignum_st
+{
+BN_ULONG *d;    /* Pointer to an array of 'BN_BITS2' bit chunks. */
+int top;    /* Index of last used d +1. */
+/* The next are internal book keeping for bn_expand. */
+int dmax;   /* Size of the d array. */
+int neg;    /* one if the number is negative */
+int flags;
+};
+#endif
+
 void Connector::readEFSOD() {
     auto content = readFileBySFI(EFSOD_SFI);
     bytes digest(256 / 8);
@@ -494,7 +515,7 @@ void Connector::readEFSOD() {
 
     bytes encapsulatedDigest(256 / 8);
     SHA256(encapsulatedBytes.data(), encapsulatedBytes.size(), encapsulatedDigest.data());
-    logBytes("FILE SOD encapsulated digest %s", encapsulatedDigest);
+    logBytes("FILE SOD calculated encapsulated digest %s", encapsulatedDigest);
 
     auto signer = (PKCS7_SIGNER_INFO*)sk_value((OPENSSL_STACK*)pkcs7->d.sign->signer_info, 0);
 
@@ -507,7 +528,7 @@ void Connector::readEFSOD() {
         if (ASN1_TYPE_get(x) == 4) {
             auto p = x->value.octet_string;
             auto pp = bytes(p->data, p->data + p->length);
-            logBytes("%s", pp);
+            logBytes("sod stored message digest %s", pp);
 
             if (pp != encapsulatedDigest) {
                 throw "Encapsulated digest check with attribute data wrong";
@@ -516,10 +537,62 @@ void Connector::readEFSOD() {
     }
 
     { // now use openssl to verify with no CA
-
+        // If PKCS7_NOVERIFY is set the signer's certificates are not chain verified.
+        int simple_verify = PKCS7_verify(pkcs7, nullptr, nullptr, nullptr, nullptr, PKCS7_NOVERIFY);
+        LOGI("certificate basic check status %d", simple_verify);
     }
 
-    { // extract certificate and check with CA pubkey
+    { // extract certificate's signature and check with CA pubkey
+        auto cert = (X509*)sk_value((OPENSSL_STACK*)pkcs7->d.sign->cert, 0);
+        const ASN1_BIT_STRING *psig;
+        const X509_ALGOR *palg;
+        X509_get0_signature(&psig, &palg, cert);
 
+        bytes signature(psig->data, psig->data + psig->length);
+        logBytes("signature raw %s", signature);
+
+        const unsigned char* sig = signature.data();
+        ECDSA_SIG* cert_sig;
+        d2i_ECDSA_SIG(&cert_sig, &sig, signature.size());
+
+        if (!cert_sig) {
+            throw "cannot get certificate signature";
+        }
+
+        LOGI("certificate get successfully");
+
+        LOGI("certificate signature: (%s,%s)\n",
+               BN_bn2hex(ECDSA_SIG_get0_r(cert_sig)),
+               BN_bn2hex(ECDSA_SIG_get0_s(cert_sig)));
+
+        bytes tbs(1000);
+        unsigned char* tbsPtr = tbs.data();
+        int tbsSize = i2d_re_X509_tbs(cert, &tbsPtr);
+        printf("%d\n", tbsSize);
+        logBytes("tbs %s", tbs);
+
+        bytes tbsDigest(384 / 8);
+        SHA384(tbs.data(), tbsSize, tbsDigest.data());
+        logBytes("digest %s", tbsDigest);
+
+        // ca params
+        BIGNUM* ca_x = nullptr;
+        BIGNUM* ca_y = nullptr;
+        BN_dec2bn(&ca_x, "5705586746797687392276527904990313555022905475611271258729414636068323857880334000957361424951661974682935706611888");
+        BN_dec2bn(&ca_y,  "7821704373206592378644977211567592118672246135776362491204878202396889655625917188376232816427307041739256606332695");
+
+//        printf("ca pubkey: (%s,%s)\n",
+//               BN_bn2hex(ca_x),
+//               BN_bn2hex(ca_y));
+
+        EC_KEY* ca = EC_KEY_new_by_curve_name(NID_secp384r1);
+        EC_KEY_set_public_key_affine_coordinates(ca, ca_x, ca_y);
+
+        bool ca_verify = ECDSA_do_verify(tbsDigest.data(), tbsDigest.size(), cert_sig, ca);
+        LOGI("ca verified status %d\n", ca_verify);
+
+        if (ca_verify != 1) {
+            throw "verification with CA returns false";
+        }
     }
 }
\ No newline at end of file